1. Field of the Invention
The present invention relates to an apparatus for securing boxes of merchandise to a wooden pallet through the use of a continuous stretch wrap layer applied to the exterior of the loaded pallet. The invention also relates to an improved rotating arm mechanism utilized with the apparatus to achieve a proper wrap. More specifically, the invention relates to a multi-station wrapping mechanism which utilizes a single wrapping mechanism to wrap pallets at more than one location and to travel along a beam between the stations.
2. Description of the Prior Art
Modern transportation methods of goods involve the packaging of discrete manufactured units within cardboard enclosures. These cardboard enclosures are frequently stacked on a wooden pallet in standard lot sizes for ease of transportation in large quantities. The pallets are adapted to be easily located and transported through use of a forklift and may furthermore may be transported along a conveyor. Because the palleted merchandise must be moved by mechanical means, often involving stopping, starting and changing directions, the palleted load must be secure upon the pallet A first method of securing the load is to stack the objects thereon in an interlocking pattern which maximizes the stability of the stacked load. The weight and location of the goods are evenly distributed on the pallet so that minimal shifting occurs during transportation. Furthermore the pallet pattern, as such stacking practices are called, is designed to prevent collapse of materials in the lower portion of the stack.
An additional method for securing the "palletized" materials to the pallet is to enclose the palletized stack in a plastic wrap or film. This is especially useful when all of the palletized materials are not of identical shape and size. A plastic stretch wrap is applied to the exterior of the pallet stack and continuously wrapped around the exterior of the stack to effectively form a solid cube of materials. Due to the weight and size of the now unitary structure mounted on the pallet, shifting is less likely to occur during transportation of the palletized merchandise. In order to apply the stretchable plastic wrap to the pallet, the wrap is pre-stretched to a specified limit, applied to the palletized stack of merchandise with a certain force, and allowed to shrink back against the exterior of the palletized stack, forming a tight enclosure around the stacked materials. The physical wrapping of the pallet stack usually involves a helical progression of wrap from top to bottom, or vice versa, in a repeated fashion until the stack has been adequately secured. Care must be taken that the wrap is applied with the proper amount of pre-stretch and tension, commonly known as force to the load, otherwise the stack may become unstable or the contents may be crushed by the force of the stretched film
A number of devices have been proposed in the prior art to automatically perform this wrapping function. A representative sample of these devices are disclosed in Ball, et al., U.S. Pat. No. 4,722,170, issued Feb. 2, 1988; Salzsauler, U.S. Pat. No. 4,934,123, issued Jun. 19, 1990; and Haloila, U.S. Pat. No. 4,993,209, issued Feb. 19, 1991. Each of the references discloses a device which generally comprises a support stand having a rotating swing arm mounted thereon, and a swing arm having a carriage at the end thereof which contains the plastic wrap. The Haloila reference utilizes a fixed circular track surrounding the pallet having a carriage mounted thereupon, to achieve the same objective. The carriage containing the plastic wrap is continuously rotated in a circular fashion about the palletized stack which is helically encased in at least one layer of film while the carriage rotates thereabout while moving vertically along its support column.
Each of the previously described devices is stationary and permanently mounted within its operating environment. None of the previously mentioned three references describes the method by which the palletized materials are brought to the location of the wrapping device.
Buettner, U.S. Pat. No. 3,930,442, issued Jan. 6, 1976; Shulman, U.S. Pat. No. 4,109,445, issued Aug. 29, 1978; and Haloila, U.S. Pat. No. 4,936,080, issued Jun. 26, 1990, all disclose similar wrapping devices as those previously described. Each of these three references further discloses the use of a conveyor to transport the palletized goods to the wrapping station.
In practice, the cost and speed of these prior art devices necessitates the use of a single wrapping device in conjunction with a plurality of conveyor feed lines. In most packaging operations, a number of stacked pallets are prepared simultaneously and must be conveyed to the single wrapping device. Feed conveyor lines are utilized to transport the stacked pallet to the wrapping device. Since multiple feed lines are utilized, the feed lines must be sequentially combined into a single line leading to the wrapper. The complexity of this transportation system including changes in direction of the palletized material. Furthermore, the transportation of a stacked pallet from one feed line to another provides a great opportunity for the disintegration of the palletized load. This is especially prevalent when the palletized load comprises a large number of small boxes or boxes of varying size and weight. In such a stack, the lightest, smallest boxes are placed at the top of the palletized stack and are more likely to be lost or damaged during transportation of the stack on the conveyors.
What is lacking in the art, therefore, is a device which minimizes the amount of transportation distance between the palletizing of the goods and the wrapping thereof. Furthermore, a device is lacking in the art which minimizes the complex twists and turns a palletized load must undergo between the creation thereof and the wrapping by the wrapping apparatus.